2112
H. STEINFIXK A N D G.D. BRUNTON
Inorganic Chemistry, Vol. 9,N o . 9,1970
Possibly the energy required to deform even slightly the five-membered chelate ring in 3 upon formation of its anionic intermediate is responsible inasmuch as the ester oxygens in Cu(Etala-sal)2 are coordinated weakly or not a t all. l6
Acknowledgment.-This research was supportecl by the Kational Institutes of Health under Grant G l f 15471. \Ye thank Dr. E. H. Abbott for a preprint of ref 22 and Dr. D. A. Buckingham for a copy of the thesis cited in footnote 36.
COXTRIBUTION F R O M THE MATERIALS SCIEhCE LABORATORIES, DEPARTMEKT O F CHEMICAL ESGINEERING, UNIVERSITY O F TEXAS A T AUSTIN, AUSTIN,T E X A S 78712, A S D THE REACTOR CHEMISTRY DIVISION, OAK RIDGENATIONAL LABORATORY, OAK RIDGE,TENNESSEE 37830
The Crystal Structure of Erbium Oxalate Trihydratel BY H. S T E I N F I S K
AND
G. D. BRUKTON
Received May 26, 1969 The compound Er(C204)(HC%Od) ,3H20 crystallizes in space group P4/n with a0 = 8.6664 (3) k and co = 6.4209 (8)A a t 24'. The measured density is 2.8 (1)g/cm3 and the calculated density is 2.742 g/cm3 so that there are two formula weights in the unit cell. Molybdenum radiation was used to measure the integrated intensities of 1641 independent reflections with a scintillation counter and a four-circle diffractometer. The parameters were refined by least squares t o R = 0.072 using anisotropic temperature factors for all atoms except for the water molecules. The erbium atom is coordinated t o eight oxygen atoms a t distances of 2.362 (5)-2.418 (5) b and they form a distorted square antiprism around the cation. A water molecule forms the ninth near neighbor a t 2.441 (9) A above the larger square face of the antiprism. The acid oxalate a n d oxalate anions occupy crystallographic sites a t random. The "statistically averaged" oxalate group is centrosymmetric a n d planar with C-C = 1.529 (11)A, C-0 equivalent to C=O equals 1.264 (7) .$; the values of the angles are 0(1)-C-0(2) = 125.9 ( 5 ) ' , O(1)-C-C = 116.8 ( 7 ) ' , and 0(2)-C-C = 117.3 (6)". Hydrogen bondingexists bttween HzO(1) and the oxygen atoms of the acid groups a t distances of 2.73 (7) A. A very short hydrogen bond, 2.43 (4)A, is observed between two HzO(2) molecules but the physical significance is difficult to assess because HsO(2) is disordered in this structure. This compound occurs also for dysprosium, ytterbium, and yttrium analogs but could not be prepared for neodymium.
Introduction The rare earth oxalate hydrates Ln2(C204)3 10H20 (Ln = La, Nd, Gd) have been prepared and characterized optically2 and by X-ray diffraction powder data2y3which show that they are isomorphous. Some of the transuranic elements also form these oxalate hydrates and are isomorphous with the rare earth compound^.^ No comparable oxalate hydrates for the heavy rare earth elements have been reported. Dr. R. H. Karraker of Eastern Illinois University undertook the preparation of oxalates of the heavy rare earths. It was observed that the powder X-ray diffraction diagrams of his oxalate preparations were different from the previously reported patterns for the lanthanide oxalate decahydrates and an analysis of the erbium compound indicated that the material has the formula Er(HC204)(C204) .3H20. The complete crystal structure analysis of this compound was undertaken because no structural investigation of a rare earth oxalate has been reported and because these materials contain both the acid monoanion and the dianion in the same structure. The presence of a dicarboxylic acid molecule together with its doubly charged ion has recently been reported for potassium hydrogen malonate. 4 , 5 Oxalic (1) Research sponsored by t h e U. S. Atomic Energy Commission under contract with t h e Union Carbide Corp. ( 2 ) V. Gilpin a n d W, G. McCrone, A n d . Chem., 24, 225 (1952). (3) I. L. Jenkins, F. H. Moore, and M . J. Waterman, J. Inoug. N z d . C h r m . , 27, 77 (1965). (4) K. Parthasarathy, Science, 161, 179 (1968). ( 5 ) R. Parthasarathy, J . G. Sime, and J . C . Speakman, Aclrb Cvyrtullogi ., Sect. B,26, 1201 (1969).
acid has different bond lengths for C=O and C-OH6-* and we planned to identify the bonding that exists between the cation and the two different anions. Also, the oxalate ion is not always planarQand the conformation of the oxalate ion in this compound is therfore also of interest. Experimental Section Erbium oxalate trihydrate, Er(HCgO4)(Cn01).3H20, was prepared by precipitating erbrium oxalate from an aqueous solution of erbium chloride and oxalic acid. The erbium oxalate precipitate was redissolved in concentrated HCI and pink crystals were grown by evaporating the HC1 slowly a t room temperature. After about 1 week good crystals were obtained. A similar technique was used to prepare the Dy, Yb, and Y analogs of the erbium compound but the Nd isomorph could not be prepared. Results of a wet chemical analysis of the crystals follow (as weight per cent). Anal. Calcd for ErlHC204)(C204).3H~O: Er, 41.99; oxalate, 44.45; E-120, 13.56. Found: E r , 40.8; oxalate, 43.6; H n O , 15.4. Precession photographs of a crystal show the diffraction symmetry 4/m and the only observed systematic absences were hkO with h k = 2n f 1. Thwe absences are characteristic solely of space group P4/n (C4h, no. 85). Most of the crystals are bounded by the forms { l l O ) and (001). A crystal bounded by these forms and with dimensions 0.312 X 0.390 X 0.299 i 0.005 mm was mounted on a Picker four-circle automatic single-crystal diffractonieter. The takeoff angle was reduced to 1.2' and 32 reflection maxima between
+
( 6 ) E. G . Cox, R.1. R' Dougill, a n d G. A . Jeffrey, J . Chem. Soc., 4854 (1952). (7) G . E. Ahmed anti I). W. J. Cruickshank, Acta Cuysluliogv., 6 , 385 (1963). (8) I
